Until just a few days ago I was pretty sure that he wouldn’t. My guess was that he would negotiate some minor changes to the agreement, declare victory and move on. Markets seemed to agree...

But I’ve been revising that view in light of recent events — especially Trump’s health care temper tantrum. Breaking up Nafta would be terrible for Mexico and bad for the U.S. ... But it might be good for Trump’s fragile ego. And that’s a reason to fear the worst. ...

We now live in a North American economy built around the reality of free trade. In particular, U.S., Canadian and Mexican manufacturing are deeply enmeshed with one another. Many industrial plants were built precisely to take advantage of our economic integration, buying from or selling to other industrial plants across the borders.

As a result, breaking up or degrading Nafta would have the same disruptive effects that came from Nafta’s creation: Plants would close, jobs would disappear, communities would lose their livelihoods. And, yes, many businesses, small, large and in some cases huge, would lose many billions of dollars.

Oh, and it’s not just manufacturing. What do you think would happen to the farmers of Iowa if they lost one of the most important markets for their corn? ...

Most important, look at what Trump has been doing with his open, indeed gleeful sabotage of the U.S. health care system. Never mind the huge human costs he’s imposing; he isn’t even following any plausible political strategy, since he and his party are likely, with good reason, to be blamed for the damage. Furthermore, his actions will cost big businesses — insurers and health providers — billions; he’s even boasting about how much he has hurt their stock prices.

So we’ve now seen Trump deliberately hurt millions of people and inflict billions of losses on a major industry out of sheer spite. If he’s willing to do that on health care, why assume he won’t do the same thing on international trade policy?

Nafta, then, is at real risk. And if it does get destroyed, the only question is whether the consequences will be ugly, or extremely ugly.

Until just a few days ago I was pretty sure that he wouldn’t. My guess was that he would negotiate some minor changes to the agreement, declare victory and move on. Markets seemed to agree...

But I’ve been revising that view in light of recent events — especially Trump’s health care temper tantrum. Breaking up Nafta would be terrible for Mexico and bad for the U.S. ... But it might be good for Trump’s fragile ego. And that’s a reason to fear the worst. ...

We now live in a North American economy built around the reality of free trade. In particular, U.S., Canadian and Mexican manufacturing are deeply enmeshed with one another. Many industrial plants were built precisely to take advantage of our economic integration, buying from or selling to other industrial plants across the borders.

As a result, breaking up or degrading Nafta would have the same disruptive effects that came from Nafta’s creation: Plants would close, jobs would disappear, communities would lose their livelihoods. And, yes, many businesses, small, large and in some cases huge, would lose many billions of dollars.

Oh, and it’s not just manufacturing. What do you think would happen to the farmers of Iowa if they lost one of the most important markets for their corn? ...

Most important, look at what Trump has been doing with his open, indeed gleeful sabotage of the U.S. health care system. Never mind the huge human costs he’s imposing; he isn’t even following any plausible political strategy, since he and his party are likely, with good reason, to be blamed for the damage. Furthermore, his actions will cost big businesses — insurers and health providers — billions; he’s even boasting about how much he has hurt their stock prices.

So we’ve now seen Trump deliberately hurt millions of people and inflict billions of losses on a major industry out of sheer spite. If he’s willing to do that on health care, why assume he won’t do the same thing on international trade policy?

Nafta, then, is at real risk. And if it does get destroyed, the only question is whether the consequences will be ugly, or extremely ugly.